Primal Growth + Kicker + Conspire

[TsumiBand]

I control Wort, the Raidmother and one other Green creature. I'd like to pay the Conspire cost on Primal Growth. Can I also pay the Kicker cost?

I seem to recall some years ago that a ruling was made in regard to the "order" of paying costs due to a questionable play of playing Vengeful Dreams by discarding Riftstone Portal for the additional cost, then tapping lands for mana that could not have produced under normal circumstances (I think it was like... in a mono-black deck or something. it's a 10 year old story, not real sure).

Anyway I'm telling this story because as I recall, due to that line of play there have been rulings about the order of paying costs vs. additional costs, and I didn't know if Conspire vs. Kicker would, in this particular situation, leave one payable and one not.

[cdr]

Both conspire and kicker are optional additional costs. You can choose as many additional costs as you like.

The issue with discarding Riftstone Portal to pay a cost is that at the end of playing a spell, 5) the total cost is locked in 6) mana abilities may be used 7) costs are paid in any order. By the time you discard Riftstone Portal to pay a cost, you are past the point where you can use mana abilities.

[TsumiBand]

Both conspire and kicker are optional additional costs. You can choose as many additional costs as you like.

The issue with discarding Riftstone Portal to pay a cost is that at the end of playing a spell, 5) the total cost is locked in 6) mana abilities may be used 7) costs are paid in any order. By the time you discard Riftstone Portal to pay a cost, you are past the point where you can use mana abilities.

Ah I see the issue as it pertains to Riftstone Portal now; it's to do with the window in which a player can play mana abilities vs. paying costs. That makes a lot of sense.

And I think I found the relevant rule which backs this up - costs are paid all at once, but in any order, as you've said.

601.2e The player determines the total cost of the spell. Usually this is just the mana cost. Some spells have additional or alternative costs. Some effects may increase or reduce the cost to pay, or may provide other alternative costs. Costs may include paying mana, tapping permanents, sacrificing permanents, discarding cards, and so on. The total cost is the mana cost or alternative cost (as determined in rule 601.2b), plus all additional costs and cost increases, and minus all cost reductions. If the mana component of the total cost is reduced to nothing by cost reduction effects, it is considered to be {0}. It can't be reduced to less than {0}. Once the total cost is determined, any effects that directly affect the total cost are applied. Then the resulting total cost becomes "locked in." If effects would change the total cost after this time, they have no effect.

601.2f If the total cost includes a mana payment, the player then has a chance to activate mana abilities (see rule 605, "Mana Abilities"). Mana abilities must be activated before costs are paid.

601.2g The player pays the total cost in any order. Partial payments are not allowed. Unpayable costs can't be paid.
Example: You cast Altar's Reap, which costs {1}{B} and has an additional cost of sacrificing a creature. You sacrifice Thunderscape Familiar, whose effect makes your black spells cost {1} less to cast. Because a spell's total cost is "locked in" before payments are actually made, you pay {B}, not {1}{B}, even though you're sacrificing the Familiar.